The invention relates to a resonance system with variable geometry for the fresh-gas conduit of internal combustion engines, by the aid of which filling ability of the resonance system can be improved and kept on the most optimal level even with several selected rotational speeds of the engine.
Fresh-gas conduits of internal combustion engines have been formed frequently as resonance systems, by the aid of which--in particular at low rotational speed of the engine--filling of the cylinders of the engines can be increased. Similar solutions are specified in the Patents DE-PS Nos. 1 935 155 and 2 245 732.
Solutions are also known where the resonance system consisting of the a resonance vessel and of at least one resonance pipe forms only an essential element of the fresh-gas conduit and is completed with other elements increasing filling (changing) of the cylinders. Such an element may be the suction pipe resulting in filling the suction pipe, as as disclosed, for example, in the Patent DE-PS No. 3 544 122.
Application of the resonance systems has been also known, with which not all the resonance systems built-in into the fresh-gas conduit are communicating with the suction openings of the cylinders of the engine. Such a system functioning as a so-called blind resonance system, improves filling of the cylinders (see German Patent DE-PS No. 2 949 790.
Independent of the character of assembly, the common feature of the resonance systems lies in that the most efficient filling activity can be achieved only at a defined rotational speed of the engine. In case of deviating from this value, efficiency drops. Even the r.p.m. range resulting in a still acceptable improvement does not include the complete operative r.p.m. range of the internal combustion engines. So it is quite obvious that there is a tendency to change number of revolutions--so-called r.p.m of resonance--at which a resonance system is able to yield the most advantageous effect.
In consideration that natural frequency of the oscillation of the fresh-gas flowing in the resonance system can be defined, in addition to the sound velocity of the medium, by the geometric dimensions of the resonance system, that is the resonant volume /V.sub.R /, the length of the resonance pipe (L) and by the cross-section of the resonance pipe (f), by properly selecting these dimensions the desired r.p.m of resonance can be achieved.
Character of the resonant volume is described in the German Patent DE-PS No. 3 232 366. According to this specification, the resonant volume comprises the volume of the resonator vessel, the volume of the suction channels interconnecting the resonance vessel and the suction openings of the cylinders and the average cylinder volume communicating with the resonator vessel during one oscillating period of the fresh air.
Solutions are also known, with which an expediently chosen regulator is changing continuously the volume of the resonance vessel and thus the resonant volume in compliance with requirements.
In other cases, as e.g. in accordance with the specification of the utility model JA-U2-5922249 the length of the resonance pipe is varied in order to shift resonance frequency.
A solution is also known, where the resonance vessel is connected to two resonance pipes, of which one pipe can be opened or closed with a closing device. This type is specified in the German Patent DE-PS No. 3 544 122; by this solution it becomes possible to change simultaneously the cross-section of the resonance pipe and the effective pipelength.
Common deficiency of all known solutions lies in that geometric dimensions of the resonance system can be changed so and to such an extent which suffices exclusively for changing the natural frequency of the fresh-gas flowing in the system. These solutions yield satisfactory results in acoustic oscillating systems, in which oscillating process is taking place at inconsiderable gas velocities. These solutions, however, these cannot be used efficiently with the resonance system of internal combustion engines, because in these systems--to achieve improved filling--simultaneously with pressure oscillations gas flow of considerable velocity may be observed. Accordingly, proper selection of the natural frequency of oscillations represents a necessary but insufficient condition for a satisfactory operation.
The aim of the invention is to change the geometry of the resonance system to such an extent, that not only the natural frequency can be changed in compliance with requirements, but additionally optimal function of the resonance system can be assured even with oscillations with a changed natural frequency.
The invention is based on the recognition that when using two parallel-connected resonance pipes built into the fresh-gas conduit of internal combustion engines for improving filling, three geometric characteristics (namely resonance volume, length and cross-section of the resonance pipe) affecting the resonance frequency of the resonance system can be changed with one single closing element which changes the resonant volume by disconnecting one of the pipes. It is noted that the reasonant volume does not only include the volume of the resonance vessel, but the sum of all connected volumes, in which pressure change occurs essentially simultaneously, whithout phase shift and phase lag.
Accordingly, the invention provides a resonance system with variable geometry in the fresh-gas conduct of reciprocating internal combustion engines having a resonance vessel provided with an outflow opening communicating with the suction opening of the engine cylinder, more than one resonance pipes discharge into said vessel, of which one, or in a controlled way connected in parallel, a plurality of pipes form free flow cross-section of the fresh gas and a closing element connects to or disconnects from the resonance vessel a volumetric element by closing the cross-section of the resonance pipe, thus changing the resonance frequency of the resonance system.
With the most simple embodiment of the invention the closing element is arranged in the pipe-end lying opposite to the end of one of the resonance pipes discharging into the resonance vessel. With this embodiment, in particular, if the shortest one of the pipes of different length is closed, the resonance pipe loses its pipe character and assumes a volumetric character, so the volume of the resonance pipe is to be added to the volume of the resonance vessel, when calculating resonant volume.
By closing or opening the resonant volume will change, so cross section of throughflow of the resonance pipe, through which fresh-gas is flowing into the engine, in case of resonance pipes of different length, the active length of the resonance pipe is changing too. It goes without saying that by the closing or opening first of all the resonance frequency is changing.
Accordingly, the natural frequency of the system can be adjusted to two separately chosen rotational speed of the engine and in such a manner, that at both selected natural frequencies, a gas velocity--sufficing for improved filling--arises in the open resonance pipes, enabling throughflow. The magnitude of the resonant volume changes accordingly. In such a manner for both r.p.m of resonance an advantageous volumetric ratio determined by the pneumatic oscillating system can be assured, namely between the resonant volume--(which is analogous to a pneumatic "spring")--and the volume of the resonance pipe, (which is analogous to) the "mass" consisting of the pneumatic medium.
According to a further preferred embodiment of the invention, the closing element is arranged in the resonance vessel. In its closed position that part of the volume of the resonance vessel will be disconnected, into which one of the resonance pipes opens.
According to a further preferred embodiment of the invention, the closing element is arranged in the equalizing vessel. In the closed position of the closing element that part of the volume of the equalizing vessel will be disconnected, into which one of the resonance pipes opens. It is noted that the equalizing vessel is connected to the pipe-end lying opposite to the end of the pipes connected to the resonance vessel. The equalizing vessel has an inflow opening for the fresh gas.)
By the application of the solution according to the invention it can be achieved that the resonance system assures maximal filling not only at a certain rotational speed, i.e. frequency, but it shows a similar efficiency in increasing the filling (charging) factor at another number of revolution.
In such a manner it can be achieved that at both r.p.m. of resonance requirements can be met which result in an efficient operation, namely gas velocity of satisfactory magnitude prevails in the resonance pipe delivering predetermined kinetic energy, at the same time, the co-operating resonant volume is also changing. That means that at both r.p.m. of resonance the system may be rendered optimal for improved filling of the cylinders, while known solutions are set optimally to one single resonance frequency only, which may be shifted within one range or displaced, abandoning an optimal operation for lack of proper conditions.
In case of the solution according to the invention, length and/or cross section of three resonance pipes communicating with the resonance vessel are not necessarily identical. This can be achieved so that by actuating the closing organ, i.e. by opening or closings the cross section, efficient length and volume of the resonance pipes and simultaneously the resonant volume change.
Practically this means, that to every single selected natural frequency (r.p.m. of resonance) which can be adjusted by changing geometric dimensions/conditions, any other conditions can be established, such as a given velocity of fresh-gas at the prevailing r.p.m. of resonance the, ratio of volumes etc. which guarantee optimal efficiency of the resonant system.